The present invention pertains generally to a means for projecting acoustic waves in a body of water or other liquid media, and more particularly to such apparatus having improved power efficiency.
The projection of low-frequency (5-100HZ) acoustic signals in a liquid media, such as water contained in an ocean body or in a man-made tank, is required for various purposes which are well known to persons skilled in the art, e.g. to calibrate certain types of sonar equipments. Generally, an acoustic projection system provides a piston or other radiator which is reciprocably moved to project a train of waves, wherein the frequency of the waves is equal to the frequency of reciprocation, and the power required by the system to generate the wave train is determined by the resistive and reactive load components thereupon. The resistive load component generally comprises the energy transferred by the radiator to the projected waves, and the reactive load component comprises energy expended in accelerating the mass of the radiator and the mass of water adjacent to the radiator in back-and-forth movements.
As is well known in the art, if the dimensions of the radiator of an acoustic projection system are small compared with the wavelengths of projected waves, the reactive component of the load on the system is much larger than the resistive load, whereby the efficiency of the system is quite low. Since low-frequency acoustic waves may have wave lengths in excess of 500 feet, low-frequency projection systems are very likely to be characterized by such inefficiency, and unless the inefficiency is compensated for in some manner, power required to operate such systems may have to be provided by a substantial power source. In some presently available low-frequency projection devices, power must be supplied by a ship's engine and coupled to the device through hydraulic or other large, and hence inefficent energy transfer mechanisms. Such substantial power sources and transfer mechanisms are expensive, cumbersome, and may not even be available for numerous situations requiring the projection of low-frequency acoustic waves.